Gordon Brown has been rebuked by the statistics watchdog for his "irregular and selective" use of knife crime figures.
Sir Michael Scholar, head of the UK Statistics Authority, protested that figures put out on Thursday had not been checked and warned that putting them out prematurely was "corrosive of public trust".
Both the Prime Minister and Jacqui Smith, the Home Secretary, trumpeted a report apparently showing stabbings had fallen by a quarter in areas where police stepped up searches of young people.
In a letter to Downing Street, Sir Michael warned that the statistics were not due to be published for some time and had not been checked.
There was no comment last night from either Downing Street or the Home Office.